Belt Noise Quiz

[IanXT4]

Its a lovely sunny day for fettling and over the last week or so I have been slowly getting round to do all those "under car Tasks".

A while ago I successfully changed the accessory belt as the old one had a habit of making a little noise when it was cold.

Shortly after I changed it, I noticed a faint knocking noise on idle, its just less than every second and I am not sure if it was there before ? (you struggle to hear it with the bonnet down)

Just to be on the safe side I have removed the belt again and checked all the main pulleys.

- The alternator feels fine, smooth no play

- The tensioner seems to be working fine (requires a lot of force to remove belt) and the idle pulley bearing is smooth with no play.

- The steering pump is smooth with no play but has about 1mm of end float which I understand is normal ?

- The waterpump has no leaks and the bearing felt good with no play, however, I did notice that I as I rotated it the resistance/drag from the seal did not feel totally uniform, ie it was a very slightly tighter on one spot of rotation.

I checked all pulleys for alignment with a ruler and as far as I can see they all line up.

The belt (Contitech) has very very slight scrubbing in places on its sides, but I believe this is normal.

The interesting point is the noise is a low frequency ie not the frequency of any of the pulleys, more like the frequency of belt rotation.

It definitely seems to be in the belt area more more towards the back.

I have attached a video you can hear the noise in the background, anyone got any ideas ?

http://youtu.be/bBWWZbKFLwY

[IanXT4]

Not a single response, is it something I said

Any other petrol 4.2 owners heard a similar approx 1 second low level knock/tap on warm idle coming from the belt area?

I am at a loss, I am sure the noise was not their before, my guess is the water pump but I don't understand why the noise occur approx 1 per second.

[Davrav]

Have you tried the 'screwdriver stethescope' method to try to localise the source Ian?

[anchorman]

TBH I can't hear it.

The timing belt can resonate but isn't really a problem. You sure it wasn't there before?

Regards

[IanXT4]

Many thanks for the replys, I thought I was familiar with the noise from this engine but maybe the new tight belt has a different natural noise. When I removed the new belt to check the pulleys, I started the engine with the wheel off and tried to listen near various components using two long socket extension bars as a stethoscope and there was nothing obvious. Noise seemed louder to the right side near the tensioner and waterpump, but maybe it is a natural resonance.

I will wait till to see if it ever gets louder :)

Just out of interest, has anyone ever tried changing a belt tensioner on a 4.2, clearance to get the pivot bolt out looks very tight do you have to remove the engine mount bolts and jostle the engine over/up/down ?

[auto123]

Thanks for useful info